Manufacture of ferrotitanium alloys



Patented Nov. 26, 1940 MANUFACTURE OF FER-ROTITANIUM ALLOYS John Ralph Davis, Scarsdale, and Jerome Strauss,

New York, N. Y., and Holbert Earl Dunn, Crafton, Pa... assignors to Vanadium Corporation of America, New York, Delaware No Drawing.

8"Claims.

The present invention relates to the manufacture of ferrotitanium alloys, and more particularly to the manufacture of medium carbon ferrotitanium alloys. Ferrotitanium alloys containing under .5% carbon are generally classified as low carbon ferrotitanium, those containin from .5% to carbon as medium carbon ferrotitanium, and those containing over 5% carbon as high carbon ferrotitanium. It is to the medium carbon ferrotitanium alloys, namely, those containing 0.5% to 5% carbon, that the present invention relates.

This application is a continuation-in-part of our copending application, Serial No. 114,830, filed December 8, 193.6.

Ferrotitanium alloys are added to steel in order to deoxidize it. It is desirable, particularly when deoxidizing steel having a low carbon content, to employ ferrotitanium with a carbon content sufilciently low so that it does not unduly increase the carbon content of the steel. It is also desirable to have a ferrotitanium alloy containing high percentages of titanium so that an excessive amount of the ferrotitanium need not be added in order to produce the desired deoxidation of the steel.

The present invention provides a process of reducing titanium ores with a carbonaceous reducing agent so as to produce ferrotitanium containing up to or even greater amounts of titanium, with a carbon content below 5%.

In the usual process of producing high carbon ferrotitanium, that is, ferrotitanium containing, say, 7% to 8% carbon and 15% to 18% titanium,

a charge of titanium ore such as ilmenite, steel scrap and coal is melted in an electric furnace.

The alloy so produced has a titanium to carbon ratio between about 2:1 and about 2.521. For

addition to certain types of low carbon steel,

such product does not have a high enough ratio of titanium to carbon so that it can be used without unduly raising the carbon content of the steel.

In accordance with the present invention, we add to the ordinary charge commonly employed in the production of high carbon ferrotitanium, such for example as the charge above referred to, materials which lower the carbon content and raise the titanium content. In some cases the steel scrap may be omitted from the charge.

For the purpose of lowering the carbon content,

we employ a material such as bauxite or magnesite or any other form of refractory material containing a substantial amount of one or more oxides of aluminum or magnesium. For exam- N. Y., a corporation of Application November 25, 1939, Serial No. 306,178

ple, we may employ diaspore, corundum or high magnesia dolomite but bauxite is the preferred refractory material, due to its lower cost. The most commonly available commercial bauxite contains about to A1203. However, we 5 may use refractory materials containing less than 50% A1203 or MgO, such, for example, as kaolin or bauxitic clays which contain 40% or less of A120: and correspondingly greater amounts of S102, particularly where it is desired 0 to produce ferrotitanium alloys containing sub- .stantial amounts of silicon. In describing the invention,-we shall refer to bauxite for the sake of conciseness but it is to be understood that any other refractory material containing a substantial amount of one or more of the oxides of aluminum or magnesium may be used in its place.

It is believed that the addition of bauxite to the charge serves several important functions:

(1) It produces additional slag which protects the melted or mushy charge from absorbing carbon from the electrode.

(2) It aids in forming a refractory skull or bottom of a metallic titanium composition which prevents the melt from picking up carbon from the carbon lining of the furnace.

(3) It acts to regulate the current flow from the electrode to the charge, making it more uniform, thereby providing hotter metal and a more uniform rate of reduction. It has been established in the production of ferrotitanium alloys that the hotter the alloy is, the lower is its carbon content. This is in spite of the fact that theoretically one would expect a hotter metal to pick up more carbon than a cooler one.

(4) The constant exposure to the reducing action of localized concentrations of carbon used as reducing agent-causes continual reduction of the aluminum content of the bauxite to metallic aluminum. The aluminum so reduced from the 40 bauxite aids in reducing the titanium ore.

Whether or not the functions and manner of operation ascribed to the use of bauxite are entirely fulfilled in actual practice, we have found that its use results in a medium carbon ferro- 45 titanium.

In addition to adding bauxite or other refractory material to the charge, we preferably add material containing manganese or silicon, or both. The use of a material containing manganese or 50 silicon is not indispensable in carrying out the process but is of considerable advantage, particularly where the ferrotitanium alloy is to contain. high percentages of titanium. The manganese I may be supplied in the-form of manganese ore or ferromanganese. The silicon may be added as commercial silica rock or silica sand or ferrosilicon. We believe these materials act as fluxing agents, since they definitely aid in moi-easing the titanium content of the ferrotitanium and in re ulating the content of titanium to maintain it more uniform from tap to tap than is the'case in other prior processes. We believe that these materials act in the following manner to increase the titanium content of the alloy and maintain the titanium content more constant from tap to tap. When a charge of titanium ore such as ilmenite, steel scrap and carbonaceous reducing agent, in the proportions of about is melted in an electric furnace without the use of either bauxite or manganese or silicon, the ferrotitanium alloy, as previously stated, will contain approximately to 18% titanium and 7% to 8% carbon, the titanium to carbon ratio being about 2.5:1. This is a high carbon ferrotitanium. In the production of such high carbon ferrotitanium, or in fact in the production of a medium carbon ferrotitanium, a certain proportion of the charge forms a skull or bottom on the carbon lining of the furnace. This bottom contains about 50% titanium, 10% carbon and 35% iron; that is, the titanium bears a ratio to the carbon of more than 4: 1, which is a much higher ratio than the ratio of titanium to carbon in the alloy actually tapped from the furnace. An actual analysis of a skull or bottom is as follows:

. Per cent Titanium 51.06 Silicon .98 Carbon 12.39 Aluminum 1.51 Iron 33.80

Total 99.74

We have found that the addition of a material containing manganese or silicon or both to the charge has the effect of fluxing or lowering the melting point of this high titanium bottom, so that a portion of it may be melted and mixed with the molten alloy above it, thereby increasing the ratio of titanium to carbon of the tapped alloy. This operation of lowering the melting point and flushing out the high titanium to carbon ratio bottom or skull is referred to herein as bringing up bottom.

The addition of bauxite to the charge appears to aid in the formation of the skull or bottom of high titanium to carbon ratio material, which formation of skull or bottom is referred to herein as laying down bottom. By the proper regulation of additions of bauxite and manganese or silicon, the bottom may be either laid down or brought up, or continuously laid down and continuously brought up so as to produce the desired content and ratio of titanium to carbon in the tapped alloy. In addition, the formation of this skull or bottom protects the melted alloy from contacting with the carbon lining of the furnace, thereby preventing the absorption of carbon and resulting in a medium carbon ferrotitanium.

In the application of our preferred procedure, the following is a typical mix; charged into an 800 kilowatt carbon-lined electric furnace operating at 48 volts, using a single electrode with a bottom return, the furnace being of a type commonly employed in the manufacture of high carbon ferrotitanium:

The ferrotitanium alloy tapped after melting this charge at a temperature of at least about 2000 0., say 2100-2250 0., contains about 15% to 18% titanium and about 3% to 5% carbon, theratio of titanium to carbon being from about 3:1 to

6:1. The production of this alloy is maintained until a sufficient thickness of skull or bottom has 'been produced so as to effectively prevent the alloy from absorbing carbon from the carbonlining of the furnace. The subsequent charges are then modified by the addition thereto of manganese ore or other manganese-containing or silicon-containing material. If manganese ore is employed, it may be used in the amount of about 40 pounds when a charge as described is used. It will be seen that the charge which is used after the bottom has been formed contains both bauxite and manganese ore, in addition to the usual charge of titanium ore, steel scrap and carbonaceous reducing agent. 'The bottom or skull previously formed will be substantially the composition previously referred to containing about 50% titanium, 10% carbon and 35% iron, the ratio of titanium to carbon in the bottom being approximately 4:1 to 5:1. The addition of the manganese ore brings up some of this bottom, so that the alloy tapped from the furnace contains approximately l'7% to titanium and from 2% to 5% carbon, the ratio of titanium to carbon usually approximating 4:1 to 8:1. The additions of bauxite and manganese-containin material are regulated to maintain the protecting skull or bottom in the furnace and to produce the desired composition of ferrotitanium alloy.

The temperature of 2000 C. or over which is used according to the present invention is considerably above the boiling points of aluminum or magnesium. Accordingly the metals volati-- lize at the temperatures employed, so that the aluminum or magnesium content of the ferrotitanium alloy is not substantially increased above that which it would contain if the bauxite or magnesite or other refractory material were not used. The ferrotitanium alloy will usually contain a small amount of aluminum resulting from reduction of the alumina content of the ore but this amount is not substantially increased by the use of bauxite according to the present invention. The bauxite addition will slightly increase the aluminum content of the ferrotitanium alloy but this increase is only a small proportion of the aluminum content of the bauxite.

Instead of forming the bottom of high titanium to carbon ratio material as described by eliminating the manganese-containing material from the first charge or charges, we may provide a bottom for the carbon-lined furnace by lining the furnace with material produced in a separate opera tion. For example, we may operate a furnace in the usual manner, that is at a temperature of v the order of 2000 C. or above, to produce a high or bottom of high ratio titanium to carbon ma- Tl .terial.

This skull or bottom may be left in place for the subsequent operation or may be dugout of the furnace, broken up and used as a lining material for the production of medium carbon ferrotitanium alloys of the present invention. When this method is employed, the original charge put into the furnace for the production of medium carbon ferrotitanium may contain both bauxite and manganese ore, a charge of the Rice coal 210 Subsequent charges may be of the same or similar compositions, varying slightly according to the analysis of ferrotitanium alloy desired.

Irrespective of the particular manner in which the skull or bottom of high ratio titanium to carbon material is originally formed, the bauxite may be omitted from the subsequent charges where it is not desired to maintain the carbon content relatively low. Thus, by the use of manganese ore alone in the charge, but without the use of bauxite, an alloy may be produced containing from 17% to 25% titanium and from 6% to 10% carbon. This alloy has the desired high percentage of titanium, but the carbon is too high for some purposes, the ratio of titanium to carbon being from about 2.51:1 to 35:1. On the other hand, where it is desired to maintain the carbon relatively low and it is not necessary to have the titanium over, say, 18%, the bauxite may be used in the charge without the manganese-containing material. It will be seen that the addition of bauxite alone produces a medium carbon alloy, that the use of manganese alone produces a high titanium alloy, and that the, use of both bauxite and manganese in the charge produces an alloy having high titanium and medium carbon.

Where it is desired to increase the silicon content of the ferrotitanium above that obtained with the charges described, this may be done by adding quartz or silica stone to the charge and.

By our preferred process employing both baux ite and manganese ore, in addition to the other ingredients of the charge, we may produce a ferrotitanium alloy containing from about 15% to 30% titanium, about 5% to 5% carbon, about .5% to 10% manganese, and about 1% to 10% silicon, the balance of the alloy being substantially iron. The presence of manganese in these alloys to an extent where it becomes a substantial alloy constituent rather than an incidental impurity results in dense brilliant alloys free from slag inclusions, oxide and nitride products.

In addition to the function of manganese or silicon, or both, in the production of ferrotitanium alloys in regulating or raising the titanium content of-.the alloys, the presence of substantial amounts of manganese and silicon in the alloys is of benefit when the alloys are used for treating steel. We have found, for example, that the addition to steels or irons of a ferrotitanium alloy containing substantial amounts of both manganese and silicon produces effects in respect to cleanliness, deoxidation and crystallization in the irons and steels'which are markedly different from those obtained when the ferro alloys of these elements are used independently.

Alloy-producing furnaces operated in accordance with the present invention have operated continuously for two months under these rigorous conditions without requiring a shut-down for repairs, as comparedto the 4 or 5 days normally experienced in the art. At least a part of the long life of the furnace is believed to be attributable to the use of bauxite in the charge.

In the course of 129 consecutive taps of an average weight of 370 pounds each: 15.5% of the production analyzed under 1.0% C 39.5% of the production analyzed between 2-.-3% C 21.7% of the production analyzed between 3-4% G 21.0% of the production analyzed between 45% C 2.3% of the production analyzed between 56% C or 97.7% of the total production analyzed under 5% carbon. I a While we have specifically described the preferred procedure in carrying out our invention,

it is to be understood that the invention may be of a metal of the group consisting of aluminum and magnesium in amount sumcient to materially lower the carbon content of the ferrotitanium alloy, and a material containing metal of the group consisting of manganese and silicon in amount suflicient to materially raise the titanium content of the ferrotitanium alloy, and melting the charge at a temperature of the order of at least about 2,000 C. without substantially increasing the aluminum or magnesium content of the ferrotitanium alloy above that which it would contain if therefractory material were not used.

2. In the manufacture of ferrotitanium alloys, the steps comprising adding to a charge containing titanium ore and a carbonaceous reducing agent, a refractory material containing an oxlde of a metal of the group consisting of aluminum and magnesium in amount sufiicient to materially lower the carbon content of the ferrotitanium alloy, and melting the charge at a temperature of the order of at least about 2000 C. without substantially increasing the aluminum or magnesium content of the ferrotitanium alloy above that which itwould contain if the refractory material were not used.

3. In the manufacture of ferrotitanium alloys,

the steps comprising adding bauxite in amount sufficient to materially lower the carbon content of the ferrotitanium alloy to a charge containing titanium ore, steel scrap and a carbonaceous reducing agent,.and melting the charge at a tem-- perature of the order of at least about 2000 0. without substantially increasing the aluminum content of the ferrotitanium alloy above that which it would contain if the bauxite were not used.

4. In the manufacture of ferrotitanium alloys, the steps comprising adding relatively small amounts of bauxite and a material containing a metal of the group consisting of manganese and silicon to a charge containing titanium ore and a carbonaceous reducing agent, said bauxite being in amount sufiicient to materially lower the carbon content of the ferrotitanium alloy, said metal of said group being in amount sufiicient to materially raise the titanium content of the ferrotitanium alloy, and melting the charge at a temperature of the order of at least about 2000 C. without substantially increasing the aluminum content of the ferrotitanium alloy above that which it would contain if the bauxite were not used.

5. In the manufacture of ferrotitanium alloys consisting substantially, of iron, titanium and carbon, the steps comprising adding to a charge containing titanium ore, steel scrap and a carbonaceous reducing agent, a refractory material containing an oxide of a metal of the group consisting of aluminum and magnesium in amount sufficient to materially lower the carbon content of the ferrotitanium alloy, and melting the charge at a temperature of the order of at least about 2000 C. without substantially increasing the aluminum or magnesium content of the ferrotitanium alloy above that which it would contain if the refractory material were not used.

6. In the manufacture of ferrotitanium alloys, the steps comprising adding bauxite and a material containing manganese to a charge containing titanium ore, steel scrap and a carbonaceous reducing agent, the bauxite being in amount suflicient to materially lower the carbon content of the ferrotitanium alloy, the manganese being in amount suflicient to materially raise the titanium content of the ferrotitanium alloy, and

T melting the charge at a temperature of the order of at least about 2000 C. without substantially increasing'the aluminum content of the ferrotitanium alloy above that which it would contain if the bauxite were not used.

7. In the manufacture of ferrotitanium alloys in a carbon-lined electric furnace, the steps comprising melting a charge containing titanium ore, a refractory material containing a substantial amount of an oxide of a metal of the group consisting of aluminum and magnesium, and a carbonaceous reducing agent, thereby providing a working bottom or interlining of a solidified refractory metallic titanium composition containing a higher content of titanium than the molten bath which is intermittently tapped from the furnace, and thereafter regulating the laying down and bringing up of bottomby the addition to subsequent charges of regulated amounts of said refractory material and a material containing a metal of the group consisting of manganese and silicon.

8. In the manufacture of ferrotitanium alloys in a carbon-lined electric furnace, the steps comprising melting a charge containing titanium ore, bauxite and a carbonaceous reducing agent, thereby providing a working bottom or interlining of a solidified refractory metallic titanium composition containing a higher content of titanium than the molten bath which is intermittently tapped from the furnace, and thereafter regulating the laying down and bringing up of bottom by the addition to subsequent charges of regulated amounts of bauxite and a material containing manganese.

JOHN RALPH DAVIS. JEROME STRAUSS. HOLBERT EARL DUNN. 

